This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Bacteriophage P22, one of the best studied Salmonella phages, has been the object of tremendous genetic studies for molecular biology in the past several decades and is remarkable for its converting and transducting abilities. During the virus maturation into the mature phage, it starts as a precursor, called procapsid, with scaffolding proteins inside, then the dsDNA inserts into the expanding capsid shell via one of the twelve vertices, and scaffold proteins exit. The tail attaches to this vertex to become mature and infectious. Although both structures of P22 procapsid and mature phage had been solved to subnanometer (~9 Angstrom) resolution by cryo-EM since 2003 (Jiang W. et. al., Nat Struct Biol, 2003, 10:131-5.), most of structural details still remain elusive due to the low resolution.